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United States Patent |
6,008,462
|
Soltwedel
|
December 28, 1999
|
Mar resistant, corrosion inhibiting, weldable coating containing iron
powder for metal substrates
Abstract
A weldable heat curable liquid coating composition for steel is provided
that exhibits improved mar resistance without impairing the weldability
characteristics of the coating. To this end, the composition contains a
conductive welding aid of iron dust. The weldable coating when applied to
steel and cured thereon to a dry film allows for spot welding of the
coated steel without requiring special welding equipment and techniques.
Inventors:
|
Soltwedel; Jeffrey N. (Dublin, OH)
|
Assignee:
|
Morton International, Inc. (Chicago, IL)
|
Appl. No.:
|
942220 |
Filed:
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October 1, 1997 |
Current U.S. Class: |
219/91.2; 219/91.21; 219/117.1; 219/118; 427/386; 427/388.2; 427/388.4; 523/402; 523/406; 523/442; 523/512 |
Intern'l Class: |
B23K 011/10 |
Field of Search: |
427/386,388.2,388.4
219/91.2,91.21,117.1,118
523/402,406,442,512
|
References Cited
U.S. Patent Documents
2666835 | Jan., 1954 | Elleman | 219/10.
|
2758983 | Aug., 1956 | Toulmin, Jr. | 260/40.
|
3112283 | Nov., 1963 | Hansen et al. | 260/17.
|
3406105 | Oct., 1968 | Letendre | 204/16.
|
3503882 | Mar., 1970 | Fitch | 252/62.
|
3867299 | Feb., 1975 | Rohatgi | 252/62.
|
4081423 | Mar., 1978 | Hardenfelt | 260/40.
|
4115338 | Sep., 1978 | Kobayahsi et al. | 260/29.
|
4152368 | May., 1979 | Dorfman et al. | 260/862.
|
4195014 | Mar., 1980 | Dorfman et al. | 260/45.
|
4320048 | Mar., 1982 | Harmuth | 523/333.
|
4469714 | Sep., 1984 | Wada et al. | 427/54.
|
4559373 | Dec., 1985 | Guthrie et al. | 524/440.
|
4661675 | Apr., 1987 | Guthrie et al. | 219/91.
|
5001173 | Mar., 1991 | Anderson et al. | 523/406.
|
5030816 | Jul., 1991 | Strecker | 219/91.
|
5047451 | Sep., 1991 | Barrett et al. | 523/442.
|
5082698 | Jan., 1992 | Anderson et al. | 427/386.
|
5240645 | Aug., 1993 | Strecker | 252/511.
|
5260120 | Nov., 1993 | Moyle et al. | 428/219.
|
5270364 | Dec., 1993 | Schwartz et al. | 524/106.
|
5624978 | Apr., 1997 | Soltwedel et al. | 523/402.
|
Other References
Chatterjee, K.L. et al., "Electrode Wear During Spot Welding of Coated
Steels", Welding & Metal Fabrication, pp. 110-114 (Mar. 1996).
|
Primary Examiner: Lusignan; Michael
Attorney, Agent or Firm: Benjamin; Steven C., White; Gerald K.
Claims
What is claimed is:
1. A mar resistant, weldable, liquid coating composition, which comprises a
solvent blend of:
a) an effective film-forming amount of a resin having crosslinkable
functional groups;
b) a crosslinker in an effective amount for curing said resin; and,
c) a weldably effective amount of a welding aid of finely divided
non-magnetized iron metal particles naturally oxidized on their surface,
randomly dispersed in said liquid coating,
said coating being essentially free of ferroalloy and nickel welding aids,
and said coating being capable of forming a dry coating film on a metal
substrate after curing which is weldable.
2. The composition of claim 1, which further comprises:
e) a pigment in an effective amount to impart color, lightness and opacity
to the coating film upon curing.
3. The composition of claim 2, in which:
said iron particles are present up to about 50 wt. % of total solids.
4. The composition of claim 2, in which:
said iron particles are substantially smooth irregular spheroids.
5. The composition of claim 2, in which:
said iron particles have a particle size below about 100 mesh.
6. The composition of claim 2, in which:
a plurality of said iron particles have a particle size below about 325
mesh and the balance between about 100 and about 325 mesh.
7. The composition of claim 2, which further comprises:
d) a catalyst in an effective amount to accelerate cure.
8. The composition of claim 2, which further comprises:
f) an internal lubricant comprising polytetrafluoroethylene in an effective
amount to reduce the coefficient of friction of the cured coating film.
9. The composition of claim 2, which further comprises:
g) an effective amount of a suspension agent for stably suspending said
iron particles in the liquid coating.
10. The coating composition of claim 1, in which:
said dry weldable coating film formed after curing is an epoxy-pendant,
urethane containing compound which is the reaction product of a) said
film-forming resin comprising a mixture of at least one hydroxy-functional
polyester resin and at least one bisphenol A epoxy resin, and b) said
crosslinker comprising a mixture of at least one blocked isocyanate and at
least one aminoplast.
11. The composition of claim 7, in which:
said coating is essentially free of anticorrosive chromate pigments.
12. A method of welding, which comprises:
a) applying said weldable liquid coating composition of claim 7 onto a
metal substrate;
b) heat curing said coating to a dry film; and,
c) welding said coated metal substrate to another similarly coated or bare
metal substrate using a weld cycle similar to that for bare metal.
13. A mar resistant, weldable, liquid coating composition, which comprises
a solvent blend of:
a) an effective film-forming amount of a resin comprising a mixture of one
or more hydroxy-functional polyester resins and one or more epoxy resins;
b) an effective amount of a crosslinker for said resin which effects a
urethane cure;
c) an effective amount of catalyst to accelerate cure;
d) a weldably effective amount up to about 50 wt. % of total solids of
non-magnetized iron powder particles naturally oxidized on their surface,
randomly dispersed in said liquid coating, said iron powder particles
comprising irregular spheroids having a particle size below about 100
mesh;
e) a pigment in an effective amount to impart color, lightness and opacity
to said coating upon curing;
f) a suspension agent in an effective amount for suspending said iron
powder particles in said liquid coating,
said coating being essentially free of ferroalloy and nickel welding aids,
and said coating being capable of forming a dry coating film on a metal
substrate after curing which is weldable.
14. The composition of claim 13, in which:
said coating is essentially free of anticorrosive chromate pigments.
15. A mar resistant, internally lubricated, weldable, liquid coating
composition, which comprises a solvent blend of:
a) an effective film-forming amount of a resin having crosslinkable
functional groups;
b) a crosslinker in an effective amount for curing said resin into a dry
coating film;
c) an internal lubricant comprising polytetrafluoroethylene in an effective
amount to reduce the coefficient of friction of said dry coating film
after curing, and,
d) a weldably effective amount of a welding aid of finely divided
non-magnetized iron metal particles naturally oxidized on their surface,
randomly dispersed in said liquid coating,
said coating being essentially free of ferroalloy and nickel welding aids,
and said coating being capable of forming a dry coating film on a metal
substrate after curing which is weldable.
16. The composition of claim 15, which further comprises:
f) a pigment in an effective amount to impart color, lightness and opacity
to said cured coating film.
17. The composition of claim 16, in which:
said iron particles are present up to about 50 wt. % of total solids.
18. The composition of claim 16, in which:
said iron particles are substantially smooth irregular spheroids.
19. The composition of claim 16, in which:
said iron particles have a particle size below about 100 mesh.
20. The composition of claim 16, in which:
a plurality of said iron particles have a particle size below about 325
mesh and the balance between about 100 and 325 mesh.
21. The composition of claim 16, which further comprises:
e) a catalyst in an effective amount to accelerate cure.
22. The composition of claim 16, in which:
said coating is essentially free of anticorrosive chromate pigments.
23. The composition of claim 16, which further comprises:
g) a suspension agent in an effective amount for stably suspending the iron
particles in the liquid coating.
24. The composition of claim 16, in which:
said dry weldable coating film formed after curing is an epoxy-pendant,
urethane containing compound which is the reaction product of a) said
film-forming resin comprising a mixture of at least one hydroxy-functional
polyester resin and at least one bisphenol A epoxy resin, and b) said
crosslinker comprising a mixture of at least one blocked isocyanate and at
least one aminoplast.
25. A method of welding, which comprises:
a) applying said weldable liquid coating composition of claim 16 onto a
metal substrate;
b) heat curing said coating to a dry film; and,
c) welding said coated metal substrate to another similarly coated or bare
metal substrate using a weld cycle similar to that for bare metal.
26. A mar resistant, internally lubricated, weldable, liquid coating
composition, which comprises a solvent blend of:
a) an effective film-forming amount of a film-forming resin comprising a
mixture of one or more hydroxy-functional polyester resins and one or more
epoxy resins;
b) an effective amount of a crosslinker for said resin which effects a
urethane cure;
c) a catalyst in an effective amount to accelerate cure;
d) a weldably effective amount up to about 50 wt. % of total solids of
non-magnetized iron powder particles, naturally oxidized on their surface,
randomly dispersed in said liquid coating, said iron powder particles
comprising irregular spheroids having a particle size below about 100
mesh;
e) a pigment in an effective amount to impart color, lightness and opacity
to said coating upon curing;
f) an internal lubricant comprising polytetrafluoroethylene in an effective
amount to reduce the coefficient of friction of said coating upon curing;
and,
g) a suspension agent in an effective amount for suspending said iron
powder in said liquid coating,
said coating being essentially free of ferroalloy and nickel welding aids,
and said coating being capable of forming a dry coating film on a metal
substrate after curing which is weldable.
Description
FIELD OF THE INVENTION
This invention relates to corrosion inhibiting organic coatings for metal
substrates, and, more particularly to weldable corrosion inhibiting
organic coatings having improved mar resistance without sacrificing
weldability, and to a method of using the same to weld two pieces of metal
together.
BACKGROUND OF THE INVENTION
For many years, corrosion inhibiting organic coatings have been applied to
metal coils or sheets prior to forming into finished articles. Designing
with prepainted metal provides the metal finisher with many benefits, such
as elimination of in-house painting operations, reduction in associated
environmental liabilities, and improvement in the quality of the paint
finish. One of the problems encountered in using prepainted metal is that
if such articles are to be assembled, they must be joined together by
adhesives or weldless fasteners, since organic coatings are insulative in
nature and are either not weldable or weldable with difficulty and only by
employing special techniques and equipment.
These techniques include spot welding with higher currents or longer weld
times. However, such unorthodox methods are time-consuming and costly.
Also, excessive temperatures are normally generated in the weld areas,
which, in turn, causes vaporization and expulsion of the metal out from
between the welding electrodes. This results in inferior welds as well as
rapid deterioration of the electrode tips. Other techniques include
decreasing the thickness of the protective film which sacrifices corrosion
protection for weldability.
Recently, there has been a growing demand for "weldable" organic coatings.
Organic coatings which are electroconductive and allow for electric
resistance welding through their cured coating films without resorting to
special equipment and techniques are said to be "weldable" or have
weld-through capability. Various types of weldable anticorrosive liquid
coatings have been proposed which typically contain conductive powdered
metals or alloys to reduce the electrical resistivity of the coating film
U.S. Pat. No. 5,001,173 (Anderson et al.) discloses some commercially
popular weldable primers which contain high concentrations of conductive
powdered ferroalloys, such as ferrophosphorous (a mixture containing
di-iron phosphide and iron phosphide), and powdered zinc.
Zinc powder alone is not considered a good welding aid. Moreover, one of
the problems encountered with ferrophos-rich weldable coatings in their
appearance. Ferrophos is a very dark gray pigment, and when provided in
the coatings in the high pigment to binder ratio necessary to impart
desired weldability, it tends to produce very dark gray colored films,
which are undesirable in certain applications. For instance, mar
resistance is almost nil and even fingernail scratches are highly visible.
In addition, the dark gray coating film tends to detract from the
appearance of any topcoat finish applied thereover. Usually, it is
necessary to topcoat at high film builds for adequate hiding or encryption
of the primer, which, in turn, is very costly. Attempts have been made to
lighten weldable primers to improve mar resistance and cryptability by
adding standard light colored pigments, such as titanium dioxide, without
much success. The standard pigments are inhibitively insulative, and the
high pigment concentration needed to offset the darkness tends to impair
weldability.
One solution to this problem has been to return to the use of standard
non-weldable mar resistant coatings. Yet without welding aids in the
formulations, the very thin films (i.e., no greater than about 0.1 mil
thick) required for weldability is usually below the minimum thickness
needed to provide adequate film opacity and corrosion resistance. Another
approach taken has been to use a two-coat weldable primer as disclosed in
U.S. Pat. No. 5,260,120 (Moyle et al.), wherein a ferrophos-rich primer is
top coated with an extremely thin layer of a non-weldable, titanium
dioxide-rich, protective coating. The thin protective film provided does
not significantly interfere with the weldability of the conductive primer,
yet provides a light colored surface film which has greatly improved mar
resistance. The protective film also smooths out the abrasiveness of the
underlying ferrophos primer. However, it is time-consuming and costly to
employ such a two-step coating procedure.
Another problem encountered with weldable ferrophos-rich primers is their
abrasiveness, which raises excessive stamping and forming die wear
concerns during metal finishing operations. The abrasive, sandpaper,
texture of the film finish is due to the hardness of the ferrophos. As
mentioned above, the Moyle et al. patent provides a solution to this
problem but again requires an undesirable two-step coating procedure.
A further problem with ferrophos-rich primers is that during welding they
produce toxic fumes, such as phosphine gas, along with objectionable odors
when subject to the required welding temperatures. While the toxicity does
not reach the environmentally harmful and physiologically unsafe levels,
workers have been known to complain about unpleasant odors produced during
welding. It is difficult, or course, to reduce toxic effluents and
eliminate unpleasant odors produced by ferrophos primers without
sacrificing weldability.
Still another problem encountered with ferrophos-rich primers is that the
film finish has a very high coefficient of friction. During metal
finishing, the stamping and forming dies tend to scape off the coating
film. Corrosion protection in these areas is thus lost. Also, the paint
scrapings tend to build-up and eventually cause the finishing line to shut
down. Internal lubricants, such as polytetrafluoroethylene, have been
incorporated in conductive coatings to lower surface friction, allowing
the finishing operations to proceed without destroying the coating, as
disclosed in U.S. Pat. No. 5,624,978 (Soltwedel et al.).
Weldable primers also invariably shorten the life of the welding
electrodes. Copper tipped electrodes on resistance spot welders are easily
degraded by coating pick-up during welding. The number of spot welds that
can be made on precoated metal before corrective action is required is
dramatically reduced in comparison to that for bare metal. This results in
reduced productivity arising from the need to change or dress the
electrodes more frequently as well as inconsistent weld quality. Weldable
coatings which extend the electrode life are continually being sought.
Other types of weldable liquid coatings have been disclosed which contain
metallic welding aids other than ferrophos or zinc powders, but all of
them suffer from drawbacks. For example, U.S. Pat. No. 5,047,451 (Barrett
et al.) discloses a weldable liquid anticorrosive primer containing a
welding agent of powdered nickel, a non-weldable corrosion inhibitor of
powdered aluminum or stainless steel, a polyethylene suspension agent for
preventing the finely divided metal from settling out, a silane-treated
silicon dioxide thixotropic agent, a drawing agent of
polytetrafluoroethylene, and a hygroscopic agent. Nickel powder, however,
is dark gray and thus undesirable for improving mar resistance and topcoat
crypt. Nickel powder is also an expensive material and uneconomical for
use in weldable coatings.
Earlier U.S. Pat. No. 2,666,835 (Elleman) discloses a weldable liquid
anticorrosive zinc chromate primer containing up to 30 vol. % of primer
solids of a non-oxidized, magnetic, metal powder, such as non-oxidized
forms of nickel powder, soft iron powder, stainless steel powder, steel
powder, and nickel alloy powder. Nickel powder, however, is clearly
preferred due to its inherent possession of magnetic remanence, which
causes the metal particles to naturally link together and form conductive
chains in the paint film. While coatings containing soft iron powder are
mentioned, Elleman suggests the need for chemically reducing the thin
oxide layer normally present on iron powder before incorporating it in the
coating. This special procedure, for inclusion of only substantially
non-oxidized soft iron powder, is time-consuming and costly.
Elleman also resorts to other special techniques for generating the
weldable coating. For instance, Elleman suggests the need to expose the
liquid coating to a magnetic field prior to drying on metal, in order to
uniformly align the metal particles and thus impart the necessary
conductivity to the film. This adds a time-consuming step to the welding
process which, in turn, leads to reduced productivity and increased costs.
These primers also require zinc chromate. While chromate pigments,
including zinc chromate, strontium chromate, calcium chromate, and lead
chromate, are excellent corrosion inhibitors, they are bright yellow
insulative pigments and tend to produce darker coatings having reduced mar
resistance and higher topcoat crypt.
What is needed is a weldable liquid corrosion inhibiting coating which
forms a dry, electroconductive film on metal substrates which has improved
mar resistance, improved topcoat crypt, reduced abrasiveness, reduced
friction, reduced toxic and unpleasant odor emissions, extended electrode
life, without sacrificing weldability and corrosion resistance, and that
can weld together, in its cured state, two pieces of metal, such as steel,
coated with the same, without the need for special equipment and
techniques.
SUMMARY OF THE INVENTION
It is an object of this invention, therefore, to provide a weldable liquid
coating for metal substrates, such as steel, which does not suffer from
the foregoing drawbacks.
It is another object of this invention to provide a weldable coating that
has improved mar resistance and topcoat crypt without sacrificing
weldability and corrosion protection.
Still another object of this invention is to provide a weldable coating
that has a relatively non-abrasive texture to prevent die wear.
Yet still another object of this invention is to provide a weldable coating
that has a low coefficient of friction to prevent destruction of the
coating film during metal finishing.
And another object of this invention is to provide a weldable coating that
emits low levels of toxic effluents and unpleasant odors during welding.
A further object of this invention is to provide a weldable coating that is
weldable without rapidly deteriorating the life of welding electrodes.
It is a still another object of the present invention to provide a weldable
coating that has excellent corrosion resistance.
It is a related object to provide a method of welding together metal
articles having coated and cured thereon a weldable coating of the
aforesaid character without the need for special equipment or techniques.
The aforesaid and other objects are achieved by providing a weldable liquid
coating composition for metal in which a welding aid of conductive iron
powder is incorporated in the liquid coating to impart weldability without
substantially darkening the coating, such that when the coating is applied
and cured on a metal substrate, the coating film not only has improved mar
resistance and crypt, but also allows the coated metal to be electric
resistance welded without requiring special welding equipment and
techniques. The iron powder particles found most useful are shiny and
smooth irregular spheroids produced by water jet atomization. No chemical
reduction of the iron powders is required immediately prior to
incorporation into the liquid coating. Furthermore, the iron powders
require no magnetization and remain randomly oriented in the liquid
coating.
The preferred weldable liquid coating composition of this invention
comprises a solvent-borne, thermosetting, epoxy-pendant, urethane coating
which is characterized by a solvent blend of: a) a film-forming
hydroxy-functional resin, preferably a mixture of hydroxy-functional
polyester resins and bisphenol A epoxy resins; b) a crosslinker for the
resin which effects a urethane cure, preferably a mixture of blocked
isocyanate resins and aminoplast resins; c) a catalyst; d) a weldably
effective amount of conductive iron powder particles of the aforesaid
character randomly dispersed in the liquid to impart desired weldability
to the coating film; e) optional yet preferred suspension aid to prevent
the iron powder particles from settling out; f) optional yet preferred
internal lubricant comprising polytetrafluoroethylene to lower the
coefficient of friction of the film; and, g) minor amounts of insulative
light colored pigments, wherein the composition is further characterized
in that it is free of ferrophos and other ferroalloy and nickel welding
aids, and it may also be free of non-weldable anticorrosive chromate
pigments.
This weldable coating not only has improved mar resistance and cryptability
without sacrificing weldability and corrosion protection, but also
exhibits reduced abrasiveness for preventing excessive die wear during
finishing, reduced coefficient of fraction to prevent destruction of the
film during finishing, emits few toxic effluents and unpleasant odors
during welding operations, sustains the life of the copper-tipped welding
electrodes, and has the ability to weld together two pieces of coated
metal using a weld cycle similar to that for bare steel,
The aforesaid and other objects are also achieved by using the liquid
coating of the aforesaid character to weld together two pieces of metal.
The liquid coating is applied to metal sheets or coil and heat cured
thereon to form a hardened dry film. Two pieces of coated metal are then
welded together, for example, using a standard spot welder, without
requiring special equipment and techniques.
The various objects, features and advantages of the invention will become
more apparent from the following description and appended claims.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
Throughout this specification, all parts and percentages specified herein
are by weight unless otherwise stated.
In this invention, a weldable corrosion inhibiting coating composition in
liquid form is applied to a metal substrate. The liquid coating is
converted to a solid dry film which is bonded to the metal substrate by
heating at elevated temperatures. The heating evaporates the solvents in
the liquid layer and initiates curing of a film-forming resin to provide a
weldable protective coating film permanently adhered to the substrate.
FILM-FORMING RESIN
The weldable coating composition of this invention includes a film-forming
resin component. A wide variety of traditional film-forming resins may be
employed in this invention, such as polyester, epoxy, urethane, acrylic
and methacrylic resins. These resins generally include a plurality of
crosslinkable functional groups to initiate curing into a dry film.
The preferred resin component is a hydroxy-functional resin.
Hydroxy-functional resins provide the building blocks for producing
flexible urethane coatings, which are desired in this invention.
One suitable class of hydroxy-functional resins useful herein include
hydroxy-functional polyester resins. These polyester resins can be
prepared by any of the methods well known to those of ordinary skill in
the art. For example, condensation reactions can be carried out between
one or more aliphatic or cycloaliphatic di- or polyhydric alcohols and one
or more aliphatic, cylcoaliphatic, or aromatic di- or polycarboxylic
acids, or corresponding anhydrides.
Among the polyester resins which are useful herein are linear polyesters
derived from aromatic dicarboxylic acids and alkylene glycols. Examples of
suitable aromatic dicarboxylic acids include terephthalic acid, bibenzoic
acid, ethylene bis-p-oxy benzoic acid, tetramethylene bis-p-oxy benzoic
acid, 2,6-naphthalic acid, orthophthalic acid, and isophthalic acid.
Mixtures of terephthalic acid and isophthalic acid are particularly
useful. Examples of suitable alkylene glycols include ethylene glycol,
trimethylene glycol, pentamethylene glycol, 1,2-propanediol,
1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol,
1,4-cyclohexanedimethanol, and polyethylene glycol.
The linear polyesters can also be derived from mixtures or aromatic
dicarboxylic acids and aliphatic dicarboxylic acids and alkylene glycols.
Examples of suitable aliphatic dicarboxylic acids include maleic acid,
fumaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid,
azelaic acid, oxy-dibutyric acid, 5-oxa-1,10-decanedioic acid, 4-n-propyl
suberic acid, dodecane dioic acid, and tridecane dioic acid.
The relative amounts of aromatic dicarboxylic acid and aliphatic
dicarboxylic acid may be varied in order to obtain polyesters having
different characteristics. In general, the ratio of aromatic acid to
aliphatic acid will be from about 2:1 to 1:2 and more often about 1:1 on
an equivalent weight basis. The ratio of dicarboxylic acid to dihydric
alcohol also may be varied, however, with the diol generally being present
in excess. The ratio of dicarboxylic acid to diol is generally from about
1:1 to 1:2 on a weight equivalent basis.
The reaction between the dicarboxylic acid mixture and dihydric alcohol
mixture is effected in the conventional manner, typically by heating the
mixture to an elevated temperature in the presence of catalysts. Tin
catalysts are especially useful, including dibutyltin oxide and dibutyltin
dilaurate. Antimony oxide may also be used as a catalyst.
The hydroxy-functional polyesters prepared in this manner will generally
have molecular weights ranging between about 5,000 and 50,000, and will
further have hydroxyl numbers of between about 5 and 35.
In a preferred embodiment, the polyester resin comprises between about 20
and 60 wt. % of total solids, and, more preferably, between about 35 and
45 wt. %.
The film-forming resin component of the weldable coating composition may
also contain other resins that are capable of modifying the properties of
the polyester-rich blend, such as epoxy resins, which improve the adhesion
and flexibility of the coating film, through incorporation of pendant
epoxy groups in the urethane compound. Epoxy resins generally refer to the
condensation reaction products of an epihalohydrin and a
hydroxy-containing compound or a carboxylic acid. The epoxy resins may be
of the ether- or ester-types, although the ether-type epoxy resins are
preferred.
Ether-type epoxy resins are formed by reacting an epihalohydrin, such as
epichlorohydrin, and a compound containing at least two free alcoholic
hydroxyl and/or phenolic hydroxyl groups per molecule. The condensation
reaction is typically carried out under alkaline conditions, or, in the
alternative, in the presence of an acid catalyst. The products of such
reactions are generally complex mixtures of glycidyl polyethers.
The ether-type epoxies can be derived from aliphatic alcohols, such as
ethylene glycol, diethylene glycol, and higher poly(oxyethylene) glycols,
propane-1,2-diol and poly(oxypropylene)glycols, propane-1,3-diol,
poly(oxytetramethylene) glycols, pentane-1,5-diol, hexane-2,4,6-triol,
glycerol, 1,1,1-trimethylolpropane, pentaerythritol, sorbitol; from
cycloaliphatic alcohols, such as resorcitol, quinitol,
bis(4-hydroxycyclohexyl)methane, and 2,2-bis(4-hydroxycyclohexyl)propane;
and, from alcohols having aromatic nuclei, such as
n,n'-bis(2-hydroxyethyl)aniline and
p,p'-bis(2-hydroxyethylamino)diphenylmethane. The esters may also be made
from mononuclear phenols, such as resorcinol and hydroquinone; from
polynuclear phenols, such as bis (4-hydroxyphenyl) methane (bisphenol F),
4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl)sulfone,
1,1,2,2-tetrakis(4-hydroxyphenyl)ethane, 2-2-bis(4-hydroxyphenyl)propane
(bisphenol A), 2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane; and, from
novolaks formed from the condensates of aldehydes, such as formaldehyde,
acetaldehyde, chloral, and furfuraldehyde, with phenol, chlorinated
phenols, such as 4-chlorophenol, 2-methylphenol, and 4-tert-butylphenol.
Particularly preferred epoxy resins useful herein are diglycidyl ethers of
bisphenol A, which are formed from the condensation reaction of
epichlorohydrin with bisphenol A in the presence of alkaline catalyst.
Bisphenol A type epoxy resins are commercially available from a wide
variety of sources. Exemplary of bisphenol A type epoxy resins include
those sold under the trade name "Epon" by Shell Oil Company. Other
desirable epoxy resins include the diglycidyl ethers of other bisphenol
compounds, such as bisphenol B, F, G and H.
Another suitable class of epoxy resins useful in the present invention are
the epoxidized novolaks, such as the epoxy cresol- and epoxy
phenol-novolak resins. Aliphatic or cycloaliphatic epoxy resins can also
be utilized in the present invention.
The epoxy resins prepared in this manner will generally have molecular
weights ranging between about 300 and 100,000 and epoxide equivalent
weights of between about 150 and 10,000.
In a preferred embodiment, the epoxy resin comprises between about 0.5 and
10 wt. % of total solids, and, more preferably, between about 1 and 2 wt.
%.
The total amount of film-forming resin in the weldable coating of this
invention is usually between about 30 and 60 wt. % of total solids, and,
preferably, between about 40 and 50 wt. %.
It will be apparent to those skilled in the art that other suitable
film-forming resins may be employed in the coating composition of this
invention, although the aforesaid resins are most preferred.
CROSSLINKER
The curing agent or crosslinker for the film-forming resin component can be
selected from a variety of curing agents traditionally known to be useful
for curing such resins. As previously mentioned, a urethane curative
system is preferred. Curing agents suitable for effecting a urethane cure
include isocyanates and blocked isocyanates, although blocked isocyanates
are most preferred.
Free isocyanates are generally not used in this invention, since the
weldable coating composition is usually coil coated onto the metal
substrate from a reservoir. The coating, therefore, should have a suitably
long pot life, such that is does not cure and harden prematurely in the
reservoir.
Blocked isocyanate resins are based on the reaction products of aliphatic,
cycloaliphatic or aromatic di- and polyisocyanates and isocyanate blocking
agents which prolong the pot life of the coating. Standard methods can be
used to prepare the blocked isocyanates, for example, by biuretization,
dimerization, trimerization, urethanization, and uretidionization of the
starting monomeric isocyanates.
Examples of suitable aliphatic diisocyanates, include 1,4-tetramethylene
diisocyanate and 1,6-hexamethylene diisocyanate. Examples of suitable
cycloaliphatic diisocyanates, include 1,4-cyclohexyl diisocyanate,
isophorone diisocyanate, and 4,4'-methylene-bis-cyclohexyl isocyanate.
Examples of suitable aromatic diisocyanates, include 4,4'-diphenylmethane
diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, and
2,4-toluene diisocyanate. Examples of suitable polyisocyanates, include
1,2,4-benzene triisocyanate, polymethylene polyphenyl isocyanate, and the
like.
The blocking agent is typically selected from those materials that react
with the functional groups of the isocyanate so as to form stable adducts
at room temperature, but that can be dissociated at elevated temperature.
Examples of suitable blocking agents, include lactams, such as caprolactam
and butyrolactam, lower alcohols, such as methanol, ethanol, and isobutyl
alcohol, oximes, such as methyl ethyl ketoxime and cyclohexanone oxime,
phenols, such as phenol, p-t-butyl phenol and cresol, and pyrazoles, such
as 3,5-dimethylpyrazole.
In a preferred embodiment, the blocked isocyanate crosslinker comprises
between about 0.5 and 10 wt. % of total solids, and, preferably, between
about 2 and 5 wt. %
In addition to the aforesaid crosslinkers, it is generally preferred to
include other crosslinkers to provide the desired final urethane film
properties, such as hardness, adhesion, flexibility and solvent
resistance. One suitable class of crosslinkers are the aminoplast resins.
Aminoplast resins are based on the reaction products of formaldehydes with
amino- or amido-group carrying compounds. A wide variety of aminoplast
resins are useful in the practice of this invention. Examples of suitable
aminoplast resins, include condensation products of aldehydes,
particularly formaldehyde, with melamine, urea, dicyanodiamide,
benzoguanamine, and glycouril. Aminoplasts which are modified with lower
alkanols having from about 1 to 4 carbon atoms are preferred. The
melamine-formaldehyde condensates of hexamethoxymethyl melamine and
butylated melamime-formaldehyde are especially preferred. The aminoplast
resins facilitate hardening of the crosslinked urethane resin backbone.
Phenoplasts and carbamates can also be used.
In a preferred embodiment, the aminoplast crosslinker comprises between
about 0.5 and 10 wt. % of total solids, and, preferably, between about 2
and 5 wt. %.
In order to achieve the outstanding properties which make these weldable
coatings particularly useful, it is desirable that the amount of
crosslinker be sufficient to substantially completely react with the
functionalities present in the film-forming resin component.
The total amount of crosslinker in the weldable coating of this invention
is usually between about 0.5 and 10 wt. % of total solids, and,
preferably, between about 2 and 5 wt. %.
Other suitable crosslinkers will be apparent to those skilled in the art.
CATALYST
The coating composition of this invention may also include a cure catalyst
or accelerator to increase the rate of the crosslinking reaction between
the film-forming resin and the crosslinker. A wide variety of catalysts
traditionally employed for urethane cure systems can be used. Examples of
suitable catalysts include tertiary amines, such as triethylene diamine,
organometallic salts, particularly organotin compounds, such as dibutyltin
dilaurate, dibutyltin dilauryl mercaptide, dibutyltin maleate, dimethyltin
dichloride, dibutyltin di-2-ethylhexoate, dibutyltin diacetate, stannic
chloride, ferric chloride, potassium oleate, and acid catalysts, such as
phosphoric acid, alkyl or aryl acid phosphates, such as butyl acid
phosphate or phenyl acid phosphate, and sulfonic acids, such as methane
sulfonic acid, benzene sulfonic acid, p-toluene sulfonic acid, naphthalene
sulfonic acid, dodecylbenzene sulfonic acid, and dinonylnaphthalene
sulfonic acid. Acid catalysts blocked with amines and pyridines are also
useful for improving shelf stability.
The catalyst is generally employed in an effective amount to initiate the
crosslinking reaction at commercially acceptable rates.
In a preferred embodiment, the catalyst comprises between about 0.1 and 1
wt. % of total solids, and, more preferably, between about 0.3 and 0.5 wt.
%.
For a further description of particularly useful liquid, urethane
film-forming, coating systems, reference can be made to U.S. Pat. Nos.
5,001,173; 5,260,120; and 5,624,978, which disclosures are incorporated by
reference herein in their entireties.
WELDABILITY AGENT
Conductive ferrous metal powder, particularly iron metal powder, is
employed in this invention as the weldability agent or welding aid.
Powdered iron is a very inexpensive material. Even more significantly,
powdered iron offers very little color to the coating, which dramatically
improves the mar resistance and cryptability of the weldable coating film
without sacrificing weldability, film opacity, and corrosion protection.
Powdered iron also reduces the abrasiveness of the finished coating, does
not cause the coating to emit high levels of toxic effluents and
unpleasant odors during welding, sustains the life of the welding
electrodes and the forming dies, and converts the coating into a
composition that has welding characteristics similar to that for bare
steel. The desired adhesion, flexibility, formability of the coating are,
furthermore, not impaired using powdered iron.
The preferred iron powder employed in this invention comprises finely
divided iron particles which have shiny, silvery, uncorroded, smooth
surfaces and are in the form of irregular spheroids, resembling ball
bearings. Such irregular spheroids are traditionally produced by water jet
atomization methods. It should be understood that the geometry of the iron
powder varies significantly with their production method.
Water jet atomization, in particular, involves the introduction of a stream
molten iron which is poured from a ladle into an atomizing chamber wherein
the stream is directed past one or more nozzles which direct pressurized
jets of water to impinge against the down pouring molten metal stream. The
stream is caused to split up into multiple droplets which rapidly cool and
coagulate, forming solid particles of iron powder that fall to the bottom
of the atomizing chamber while solidifying. The iron particles thus formed
are then collected, preferably in water, and subsequently separated from
most of the water by, for example, heated drying followed by magnetic
separation. The particles are usually screened at this point to eliminate
undesirably large particles that can be reworked. The dried particles are
then collected and passed through an annealing furnace at about
1,400.degree. F. in a reducing atmosphere of hydrogen, and the iron dust
particles are finally collected in the form of smooth, shiny, irregular
(i.e., spattered) spheroids. For a further description of water jet
atomization techniques, reference can be made to U.S. Pat. Nos. 3,764,295;
3,909,239; and, 4,274,864, which disclosures are incorporated by reference
herein in their entireties.
The preferred iron particle size is less than about 100 mesh (150 microns),
and, more preferably, less than about 325 mesh (45 microns). Commercial
powders which contain about 85 to 95% of the iron particles smaller than
325 mesh and the remainder between 100 mesh and 325 mesh are most
desirable. The apparent density of the iron powder is preferably between
about 2.85 and 3.30 g/cc. Exemplary of such atomized iron powder is that
sold under the trade name "Anchor ATW-230" by Hoeganaes of Riverton, N.J.
Iron powders can also be produced by other traditional methods which
produce spheroids, such as air atomization which gives irregular spheroids
or dissociation of iron carbonyls which gives more uniform ultra fine
spheroids. Methods which produce spongy iron particles, such as the direct
reduction of iron ore or scale are generally discouraged in this
invention, since it has been found that iron with a shiny surface are far
superior to spongy iron particles. Weldable coatings containing spongy
iron powder are not easily spot welded under standard conditions.
Moreover, a spongy, pumice-like surface tends to darken the iron powder
and consequently reduces the mar resistance of the coating films.
In a preferred embodiment, the powdered iron comprises up to about 50 wt. %
of total solids, and, more preferably, between about 30 and 40 wt. %.
The weldable coating composition of this invention is further characterized
in that no chemical reduction of the natural oxide films on the surface of
the iron powder is necessary prior to incorporation in the liquid coating.
Furthermore, the liquid coating is not subject to a magnetic field after
incorporation of the powdered iron and, therefore, the non-magnetized iron
particles remain randomly oriented in the liquid.
The weldable coating composition of this invention is even further
characterized as being essentially free of dark gray welding aids, such as
ferrophos and nickel powders.
SUSPENSION AGENT
Desirably, a suspension agent is used to ensure that the powdered iron
remains stably suspended in the liquid coating and does not settle out and
form a hard cake. A suitable suspension agent is polyamide wax. Exemplary
of such suspension agents are those sold under the trade name "Disparlon
6900-20X" by King Industries of Norwalk, Conn., which are dispersions of
swollen particles of polyamide wax in low boiling alcoholic solvents such
as xylene. Other suitable suspension agents include silicon dioxide, for
example, fumed silica, silane treated silica, phosphoric acid, alkylated
or arylated phosphoric acid, and quaternary amine treated magnesium
aluminum silicate. The suspension agents also serve as thixotropic agents
to prevent gelation of the coating before application. Silicone dioxide
additionally functions as a hygroscopic agent or water scavenger in the
coating composition.
In a preferred embodiment, the amount of suspension agent present in the
coating composition is between about 0.3 and 2 wt. % of total solids, and
preferably between about 0.4 and 0.6 wt. %.
INTERNAL LUBRICANT
An internal lubricant may be incorporated in the coating composition to
lower the coefficient of friction of the coating film.
Polytertrafluoroethylene (PTFE) is the preferred internal lubricant due to
its ability to dramatically lower the coefficient of friction of the film
finish, thus allowing metal forming and finishing without destroying the
coating film. Other halogen-containing thermoplastic polymers can also be
used, although PTFE has superior lubricant properties. Blends of PTFE and
polyethylene (PE) are also useful. Other suitable internal lubricants,
such as glycerol esters, fatty acids, fatty acid esters, fatty acid
amides, fatty acid salts, fatty alcohols, and molybdenum disulfide, may be
used as well.
Desirably, the PTFE has particles in the size ranging from about 0.01 to 30
microns, and, more preferably, from about 1 to 15 microns. Suitable PTFE
is sold under the trade name "Polyfluo 190" by Micro Powders of Scarsdale,
N.Y.
The weldable coating composition preferably contains internal lubricants,
desirably PTFE, in an amount ranging between about 0.2 and 1.5 wt. % of
total solids, and, more preferably, between about 0.5 and 1 wt. %.
PIGMENT
The weldable coating composition of this invention may also contain light
colored insulative pigment powders to further improve the mar resistance,
crypt, and opacity of the coating film, as well as to provide the desired
final appearance, yet without sacrificing the weldability of the coating.
The choice of pigment will depend on the particular color or colors
desired in the coating. The pigments may be organic or inorganic pigments,
although inorganic pigments are generally utilized. Suitable inorganic
pigments include metal oxides, especially titanium dioxide. Other metal
oxides include, zinc oxide, aluminum oxide, magnesium oxide, iron oxide,
chromium oxide, lead oxide, nickel oxide, silver oxide, tin oxide, and
zirconium oxide. Other inorganic pigments which may be utilized include
inorganic sulfides, sulfoselenides, ferocyanides, aluminates, phosphates,
sulfates, borates, carbonates and especially titanates.
The pigment can be present in the coating in reduced concentrations and
still achieve the desired mar resistance and crypt. The ability to lower
the concentration of non-weldable pigments dramatically improves the
weldability of the coating, especially at the high dry film builds desired
for adequate coverage, opacity, and corrosion protection. In this
invention, mar resistant coating film builds as high as about 1.0 mil
thick coated on each side of the metal surface remain weldable without
resorting to special equipment and techniques.
In a preferred embodiment, the insulative pigment comprises no greater than
about 25 wt. % of total solids, and, more preferably, between about 10 and
20 wt. %.
The pigment to binder ratio is usually no greater than about 2, and,
preferably, between about 1 and 1.5
CORROSION INHIBITING AGENT
The coating composition of this invention may also contain a corrosion
inhibiting agent to enhance corrosion protection of the underlying metal
substrate. In this invention, a corrosion inhibiting agent is optional,
since the conductive powdered iron welding aid also serves as a
sacrificial anode and thus provides cathodic protection against galvanic
corrosion of the metal substrate.
Suitable corrosion inhibiting agents include finely divided metals, such as
powdered zinc spheroids or flakes. Typically the zinc powder is prepared
through distillation of zinc dust or by air atomization of molten zinc.
Zinc powder typically has a particle size ranging from about 1 to 15
microns, preferably from about 2 to 6 microns. Zinc powder, in particular,
improves the corrosion resistance of the coating, yet without
significantly darkening the coating film.
Other corrosion inhibitors can be employed which include anticorrosive
insulative chromate pigments, such as strontium chromate. It is generally
preferred, however, that the weldable coating composition of this
invention is further characterized as being essentially free of
anticorrosive pigments, including strontium chromate, calcium chromate,
zinc chromate and lead chromate, since these pigments impair the mar
resistance and crytability as well as weldability of the coating film.
However, in certain circumstances they may be desirable.
The corrosion inhibiting agent, desirably zinc powder, if employed, may
comprise up to about 10 wt. % of total solids, and, more preferably,
between about 3 and 10 wt. %, although it is most preferred not to employ
the same.
OTHER ADDITIVES
In addition to the above-described components, the weldable coating
composition of this invention can contain the usual functional additives
that are well known in the art, such as, the flow control agents, for
example, polyacrylic resins. Flow control agents are usually present in
amounts up to about 1 wt. % of total solids, and, preferably, between
about 0.06 and 0.5 wt. %. The polyacrylic resins generally include
methyl(meth)acrylate resins, ethylene vinyl acetate resins, and the like.
Other thixotropic agents, light stabilizers, surfactants, wetting agents,
dispersing aids, flattening agents, antioxidants, flocculating agents,
foam control agents, etc., can also be employed. Inorganic fillers, such
as calcium carbonate, may also be included in the coating. Adhesion
promoters are usually present as well in amounts up to about 0.5 wt. % of
total solids, and, preferably, between about 0.01 and 0.1 wt. %. One
suitable class of adhesion promoters are the epoxy phosphate esters, which
are generally prepared by reacting an epoxy resin with phosphoric acid.
Phosphoric acid may also be considered an adhesion promoter.
SOLVENT
The aforesaid components of the coating composition are blended together in
a suitable vehicle or carrier for the solids, such as an aqueous or
organic solvent, to facilitate formulation and liquid application.
Suitable organic solvents include aromatic and aliphatic petroleum
distillates, such as Aromatic 100, Aromatic 150, Aromatic 200, dibasic
esters (DBE), V M & P naptha, hexane, and the like, ketones, such as
isophorone, methyl ethyl ketone, methyl isobutyl ketone, methyl isoamyl
ketone, diisobutyl ketone, acetone, and the like, alcohols, such as ethyl
alcohol, propyl alcohol, diacetone alcohol, 2-ethyl hexanol, n-butanol,
and the like, dimethyl, phthalate, and mono- and dialkyl ethers of
ethylene and diethylene glycol, such as ethylene glycol monoethyl ether,
ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate,
propylene glycol monoethyl ether acetate, diethylene glycol monobutyl
ether and diethylene glycol diethyl ether, xylene, and the like. Dibasic
esters are especially useful solvents, which are typically available as
mixtures of refined dimethyl esters of adipic, glutaric and succinic
acids.
The weldable coating composition typically contains sufficient solvent to
produce the desired viscosity for the particular liquid coating method.
In a preferred embodiment, the viscosity of the uncured liquid coating
ranges preferably between about 20 and 50 #4 Zahn at 25.degree. C., and,
more preferably, between about 28 and 32.
COATING PREPARATION
The constituents of the weldable coating composition are blended together
in any convenient manner known to persons skilled in the art. Moreover, no
chemical reduction of the powdered iron is necessary before incorporation
into the liquid coating. Also, the liquid coating is not subject to a
magnetic field after incorporation of the powdered iron.
METAL SUBSTRATES
The weldable coating composition is usually applied as a primer over a
variety of metal substrates. In some cases, the primer may also serve as
the final finish. Metal substrates of current interest include zinc-,
zinc/nickel alloy, and zinc-iron alloy steels, which include various
zinc-containing forms of galvanized steel, steel having a chrome
conversion coating (with or without zinc therein) on its galvanized or
ungalvanized surface, steel having a zinc-rich primer on either of such
surfaces, and steel having FIRST COAT.RTM. aqueous epoxy resin/chromium
trioxide coating pretreatment (as described in previously mentioned U.S.
Pat. No. 5,001,173), that is commercially available from Morton
International of Chicago, Ill., baked on either of such surfaces. Other
suitable metal substrates include cold rolled and hot rolled steel,
aluminized steel, and galvanized steel such as hot-dipped and
electrogalvanized steel, galvalume, galvanneal, etc.
COATING ON METAL
The liquid weldable coating can be applied to the metal substrate by any
conventional technique, including, for example, dipping, spraying, roll
coating, and bar coating. It is preferred to use coil coating (reverse
roll coating) techniques to apply the coating.
After application, the weldable coating is heat cured and dried in an oven
to a hardened cured film finish on the substrate surface. The wet coating
is usually cured at elevated temperatures of between about 390 and
500.degree. F. peak metal temperature, and, preferably, between about 435
and 485.degree. F., for a suitable period of time to fully cure the
coating, usually between about 20 and 60 seconds, and, preferably, about
40 seconds.
The weldable coating is generally applied on the substrate in sufficient
amounts to provide a dry film coating having a thickness of up to about
1.0 mil on each surface, and usually between about 0.4 and 0.6 mils. It
has been advantageously found that two pieces of metal can be coated on
both sides with about 1.0 mil of coating film and still be welded together
using a weld cycle similar to that for bare steel.
WELDING PRECOATED METAL
After the coating is cured, the coated metal substrates can be welded
together by any standard welding technique such as electric resistance
(spot) welding, mig welding, tig welding, and arc welding. Spot welding,
in particular, involves placing together two pieces of the precoated metal
articles to form an assembly and then inserting the assembly between two
copper-tipped electrodes of a spot welder. When the welder is turned on,
an initial squeeze cycle is performed, wherein the two coated steel plates
are further forced together between the welding electrodes. A subsequent
weld cycle is performed where sufficient current flows through the
assembly including the coating, and finally a hold and off cycle is
completed before the welding electrodes are released and the welded
assembly is removed from the machine. The formation of a nugget between
the welded parts represents an excellent weld.
Any of the standard non-weldable topcoats may be applied to the precoated
metal surfaces after welding for a decorative appearance or enhanced
corrosion protection.
The invention will be further clarified by a consideration of the following
non-limiting examples.
EXAMPLE 1
Mar Resistant Weldable Urethane Primer
The following ingredients were blended together in the order and manner
given to provide a solvent borne weldable liquid primer of this invention.
______________________________________
Ingredients Weight %
______________________________________
CHARGE TO DISPERSING MILL
30% Dynapol L-205 Polyester Solution.sup.1
9.62
TiPure R-900 (TiO.sub.2) Pigment.sup.2 8.42
AeroSil 200 Fumed Silica.sup.3 0.10
Mixed Dibasic Esters (DBE).sup.4 2.53
Panasol AN-3N Solvent.sup.5 2.05
Coroc A-620-A2 Acrylic Resin Solution.sup.6 0.17
SANDMILL TO 7 HEGMAN GRIND
RINSE SANDMILL
30% Dynapol L-205 Polyester Solution
0.82
Mixed DBE 0.82
RECHARGE TO DISPERSING MILL
THEN ADD UNDER MEDIUM AGITATION
30% Dynapol L-205 Polyester Solution
23.33
40% Mor-Ester 49001 Polyester Solution.sup.7 4.15
55% Mor-Ester 4120 Polyester Solution.sup.8 18.26
Mixed DBE 3.48
Epon 828 Epoxy Resin.sup.9 0.84
Desmodur BL 3175 Blocked Isocyanate.sup.10 1.08
Resimene 747 Aminoplast Resin.sup.11 1.29
Nacure 1051 (DNNSA) Catalyst.sup.12 0.22
10% Phosphoric Acid Solution.sup.13 0.50
Metacure T-12 (Dibutyl Tin Dilaurate).sup.14 0.10
Anchor ATW-230 Iron Powder.sup.15 20.00
Disparlon 6900-20X Suspension Agent.sup.16 0.34
ADJUST VISCOSITY
Mixed DBE 1.88
Total Weight 100.00
______________________________________
.sup.1 30% Dynapol L205 Polyester Solution is a solvent solution of 30%
Dynapol L205 polyester resin of about 15,000 molecular weight and about
5-10 hydroxyl number believed to be derived from isophthalic acid,
terphthalic acid, ethylene glycol, and neopentyl glycol, and that is
commercially available from Huls of Somerset, NJ, in DBE.
.sup.2 TiPure R900 is a TiO.sub.2 pigment that is commercially available
from DuPont of Wilmington, DE.
.sup.3 AeroSil 200 is fumed silica that is commercially available Degussa
of Ridgefield Park, NJ.
.sup.4 Mixed Dibasic Esters (DBE) is a commercial mixture of dibasic
esters that is commercially available from DuPont of Wilmington, DE.
.sup.5 Panasol AN3N is a S100 Aromatic solvent that is commercially
available from Ashland Chemical of Columbus, OH.
.sup.6 Coroc A620-A2 acrylic resin solution is an acrylic flow modifier
that is commercially available from Cook Paint & Varnish of Kansas City,
MO.
.sup.7 40% MorEster 49001 Polyester Solution is a solvent solution of 40%
MorEster 49001 polyester resin of about 35,000 molecular weight and about
9 hydroxyl number derived from terephthalic acid, isophthalic acid,
azelaic acid and ethylene glycol, and that is available from Morton
International of Chicago, IL, in MEK.
.sup.8 55% MorEster 4120 Polyester Solution is a solvent solution of 55%
MorEster 4120 polyester resin of about 13,000 molecular weight and about
20-28 hydroxyl number derived from isophthalic acid, terephthalic acid,
hexane diol and neopentyl glycol, and that is available from Morton
International of Chicago, IL, in xylene.
.sup.9 Epon 828 Epoxy Resin is a bisphenol A/epichlorohydrin based epoxy
of about 350-450 molecular weight and about 175-210 epoxide equivalent
weight, and that is commercially available from Shell Chemical Company of
Houston, TX
.sup.10 Desmodur BL 3175 is a blocked isocyanate crosslinker resin of
methyl ethyl ketoxime blocked 1,6hexamethylene diisocyanate that is
commercially available from Bayer of Pittsburgh, PA.
.sup.11 Resimene 747 is an aminoplast crosslinker resin of
hexamethoxymethyl melamine that is commercially available from Monsanto o
St. Louis, MO.
.sup.12 Nacure 1051 is a sulfonic acid catalyst of dinonylnaphthalene
sulfonic acid (DNNSA) that is commercially available from King Industries
of Norwalk, CT.
.sup.13 10% Phosphoric Acid Solution is a solution of 10% phosphoric acid
catalyst in isophorone.
.sup.14 Metacure T12 is a dibutyltin dilauarte catalyst that is
commercially available from Air Products of Allentown, PA.
.sup.15 Anchor ATW320 is atomized iron powder that contains about 95% of
the iron particles finer than 325 mesh and the remainder between about 10
and 325 mesh, that is commercially available from Hoeganaes of Riverton,
NJ.
.sup.16 Disparlon 690020X is a suspension agent of a dispersion of swolle
particles of polyamide wax in xylene that is commercially available from
King Industries of Norwalk, CT.
Two cold rolled steel panels were individually coated on each side with the
foregoing liquid weldable primer and then baked at about 450.degree. F.
peak metal temperature for about 45 seconds to yield a cured dry white
coating film of about 1.0 mils thick on each side of the two panels.
The weldabilty of the coating film deposited on the cold rolled steel
panels was determined by attempting to spot weld the two coated panels
together. The coated panels were successfully spot welded together between
copper tipped 1/4" electrodes using a weld cycle similar to that for bare
steel.
The corrosion resistance characteristics of the coating film deposited on
the cold rolled steel panels was determined by subjecting the coated
panels to a salt water spray test under test method ASTM B-117. Despite
the absence of anticorrosive chromate pigments in the primer composition,
the corrosion resistance of the coating film was similar to that for
chromated primer systems at 240 hours salt spray. The performance of the
weldable primer at 580 hours salt spray was significantly worse as would
be expected without the protection of chromates. Yet, the improvement in
mar resistance and weldability are issues that cannot be obtained with
standard chromated primer systems.
EXAMPLE 2
Mar Resistant, Internally Lubricated, Weldable Urethane Primer
The following ingredients were blended together in the order and manner
given to provide another solvent borne weldable liquid primer of this
invention.
______________________________________
Ingredients Weight %
______________________________________
CHARGE TO DISPERSING MILL
30% Dynapol L-205 Polyester Solution
10.36
Mixed Dibasic Esters (DBE) 2.47
Panasol AN-3N Solvent 2.00
TiPure R-900 (TiO.sub.2) Pigment 8.21
11-3071 Fast Yellow HGR Pigment.sup.1 0.49
Cab-O-Sil M-5 Fluffy Fumed Silica.sup.2 0.20
Coroc A-620-A2 Acrylic Resin Solution 0.17
SANDMILL TO 7 HEGMAN GRIND
RINSE SANDMILL
30% Dynapol L-205 Polyester Solution
0.98
Mixed DBE 0.98
RECHARGE TO DISPERSING MELL
THEN ADD UNDER MEDIUM AGITATION
30% Dynapol L-205 Polyester Solution
21.61
Disparion 6900-20X Suspension Agent 0.49
MIX WELL THEN ADD UNDER MEDIUM AGITATION
40% Mor-Ester 49001 Polyester Solution
4.05
55% Mor-Ester 4120 Polyester Solution 17.81
Mixed DBE 4.88
Epon 828 Epoxy Resin 0.82
Desmodur BL 3175 Blocked Isocyanate 1.05
Resimene 747 Aminoplast Resin 1.25
10% Phosphoric Acid Solution 0.49
Nacure 1051 (DNNSA) Catalyst 0.22
Metacure T-12 (Dibutyl Tin Dilaurate) 0.10
Polyfluo 190.sup.3 0.50
Anchor ATW-230 Iron Powder 19.51
ADJUST VISCOSITY
Mixed DBE 1.36
Total Weight 100.00
______________________________________
.sup.1 113071 Fast Yellow HGR is C.I. Pigment Yellow 191 (inorganic
titanate) that is commercially available from Hoechst Celanese of
Charlotte, NC.
.sup.2 CabO-Sil M5 is fumed silica that is commercially available from
Cabot Corporation of Bellerica, MA.
.sup.3 Polyfluo 190 is an internal lubricant of PTFE that is commercially
available from Micro Powders of Scarsdale, NY.
Two cold rolled steel panels were individually coated on each side with the
foregoing liquid weldable primer and then baked at about 450.degree. F.
peak metal temperature for about 45 seconds to yield a cured dry putty
yellow coating film of about 1.0 mils thick on each side of the two
panels.
The weldability of the coating film deposited on the cold rolled steel
panels was determined by attempting to spot weld the two coated panels
together. The coated panels were successfully spot welded together between
copper tipped 1/4" electrodes using a weld cycle similar to that for bare
steel.
The invention having been disclosed in the foregoing embodiments and
examples, other embodiments of the invention will be apparent to persons
skilled in the art. The invention is not intended to be limited to the
embodiments and examples, which are considered to be exemplary only.
Accordingly, reference should be made to the appended claims to assess the
true spirit and scope of the invention, in which exclusive rights are
claimed.
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